The weight of a trailer is of crucial importance in the trucking industry. Weight information is used to optimize the load at or near the vehicle's maximum capacity and to make sure that the load is evenly distributed across the vehicle axles. Even weight distribution is a major concern for public safety and highway maintenance because overloading a commercial vehicle is hazardous, reducing the truck's stability and braking ability. An overloaded commercial vehicle also causes significantly greater wear to public highways and to the vehicle itself. Therefore, Governments regulate vehicle weight by specifying a maximum legal load limit. Governments also regulate the distances between the axles requiring truck operations to take those distances into account depending on their routing through different states or countries. Another complication is that pick-up and delivery of cargo requires that the trailer height be aligned with the cargo dock of a facility where the truck will load or unload cargo from the trailer. The height of the trailer can be adjusted by sliding the rear axle group back and forth. Once the cargo is loaded or unloaded, the axle group must be moved back to the legal length before the trailer can travel the roads.
The axle groups on a trailer typically include one or more axle mounted on a suspension slider so they can be moved back and forth. By moving the suspension slider back and forth the cargo weight can be distributed between the axle group(s) on the trailer and the tractor so no one axle will be over the limit. When the trailer suspension slider is moved forward (closer to the tractor) the weight is shifted from the tractor to the trailer (the trailer axle load weight becomes heavier and the tractor axle weight becomes lighter). When the trailer suspension is moved back (away form the tractor) the weight is shifted from the trailer to the tractor (the trailer axle load weight becomes lighter and the tractor axle weight becomes heavier). The truck driver may move the suspension back and forth multiple times during a route as the trailer is loaded and unloaded to comply with legal distance requirements for the separation of the axles as the truck travels from state to state and country to country.
Moving the suspension slider for the axle group back and forth to get it to the desired position is a process that requires trial and error. It typically involves several steps and considerable time to get it right. First the operator parks the tractor and trailer brakes and putting blocks in place to ensure that trailer axle group does not move during the process. Then she/he goes to the back of the trailer suspension and releases the lock/latch pins that maintain the trailer body position along a set of rails on the axle frame. Sometimes these pins become bound by the weight of the suspension and are difficult to release manually. This may require the driver to rock the trailer to disengage them. The driver must then go back into the cab, move the tractor forward or backward so the suspension slider on the trailer is in the desired position. If everything is not lined up, the operator goes back to the cab and tries again until she/he is successful. Once lined up, the operator then attempts to re-lock the pins, which could again require locking the tractor. After the desired position of the suspension is attained, the driver must go back, physically lock the pins and visually inspect the suspension.
The position of the slider is chosen from guidelines and the driver's experience based on the load and the positioning of the load so that weight is evenly distributed and distances between the axles are legally compliant. Sometimes the judgment of the driver may prove to be incorrect which could result in overweight of one axle group over another.
To simplify the process of adjusting the trailer body to the desired position on the axle frame, a device is needed that indicates to the operator when the trailer body has reached the desired pin position during the operation of sliding the trailer body along the rails on the trailer frame.
Any feature or combination of features described herein are included within the scope of the present invention provided that the features included in any such combination are not mutually inconsistent as will be apparent from the context, this specification, and the knowledge of one of ordinary skill in the art. Additional advantages and aspects of the present invention are apparent in the following detailed description and claims.